1. Field
The disclosure relates to a tire, in particular intended to bear heavy loads, such as a tire intended to equip vehicles such as heavy duty vehicles or earthmoving equipment.
2. Description of Related Art
A tire normally comprises two beads intended to come into contact with a wheelrim, a crown surmounted by a tread intended to come into contact with the ground and sidewalls connecting this crown to each bead. Furthermore, a tire is generally reinforced by a carcass reinforcement, the carcass reinforcement being anchored in each bead to a bead reinforcing circumferential element.
The term “meridian section” is understood to mean a cross section through a meridian plane passing through the axis of rotation of the tire.
Each bead comprises at least one internal annular insert, the meridian section of which is of elongated general shape and which exhibits faces joining to give a point or end (also known as apex) which is located radially outside the bead reinforcing circumferential element. The term “internal annular insert” is understood to mean an annular insert which does not exhibit a visible face when the tire is not fitted to an external wheelrim and which does not come into direct contact with the wheelrim. These bead annular inserts consist of rubber-based compositions.
The tires intended to equip vehicles bearing heavy loads at relatively high speeds, such as heavy duty vehicles or earthmoving equipment, are designed to be able to be retreaded when the tread is worn. The possibility of retreading involves having available a worn tire which has not experienced major damage, such as cracks in the semi-finished products which make up the tire. To this end, it is desirable for the cohesion of the materials forming the internal annular inserts to be as high as possible in order to prevent or reduce the risk of formation of incipient cracks which might propagate up to the external surface of the tire (it being known that the external surface of the tire denotes any surface of the tire visible to the observer when this tire is not fitted to its wheelrim).
However, it is known to a person skilled in the art that internal annular inserts are subjected to deformations at each turn of the wheel. These deformations generate high heating of the materials making up these inserts, which accelerates their thermal-chemical or thermal-oxidative ageing. This ageing has the effect of reducing the cohesion of the internal annular inserts, which is reflected by a poorer endurance of the tire.
In order to confer the best possible endurance on the tire, the internal annular insert should exhibit a sufficient level of cohesion at the start and the least possible change with use.
In order to increase the cohesion of an internal annular insert, one solution consists in increasing the content of reinforcing filler of rubber composition which forms the internal annular insert. However, this increase in the content of reinforcing filler increases the hysteresis of the rubber composition, which is reflected by a heating of the internal annular insert which is damaging to the endurance of the tire.
Thus, provision has been made to use rubber compositions of relatively low hysteresis comprising low contents of reinforcing fillers for the preparation of internal annular inserts, such as is described, for example, in U.S. Pat. No. 3,392,773 and Patent EP 1 028 007. In particular, Patent EP 1 028 007 teaches that the content of reinforcing inorganic filler in the rubber composition of an internal annular insert of a tire should not exceed 40 phr and preferably should not be greater than 35 phr, in order for the rubber composition to exhibit an optimized compromise between the cohesion and the hysteresis for the purpose of improving endurance of the tire.
Even if the endurance of the tire is improved by this solution, there still exists a need to find other solutions in order to yet further improve the endurance of the tires. In particular, it is an ongoing preoccupation for the manufacturers to find a rubber composition for such internal annular inserts which satisfies a cohesion/hysteresis compromise which makes it possible to further improve the endurance of tires, in particular bearing heavy loads.